Buried Wood Bed (sunken hugelculture) and Terrace Combo

This is my third attempt to tame the sloped area that I call as “lower garden”. It has a slope of 40-50 degrees. There is a negligible layer of topsoil, underlaying soil is mostly clay and rocks. Erosion is a major issue and roots cannot penetrate in this south facing slope. When they reach a certain height, all the trees either die in summer due to lack of water (clay gets baked) or topple over in fall/winter due to wind or snow.
It was a sun baked, bare clay eight years ago. All the topsoil was washed away. For my first attempt I covered the whole area (roughly 1 acre) with leaves, glass clippings and any organic matter that I was able to get my hands on.
I brought in many bags of leaves from nearby forest (obtaining those permits were just pain).
Covered with leaves:

I put branches over leaves to hold them down and carpet bombarded with seeds balls of all kinds of weeds and some radishes. I made mushroom slurries from all sorts of wild mushrooms and even brought in earthworms since the land seemed that it didn’t have any. I went to a public land, poured buckets of soapy water, picked the worms, gave them a clean bath and brought them to the garden. The land responded very well; weeds started to grow, and we had epic harvests of radishes, garlic, winter squashes and so on. Trees, whatever were left, ceased to die. I don’t know whether mycelium can stop trees from toppling over, but no unexpected tree falls happened since the day we started to observe mushrooms. Occasionally a sick or injured tree might come down, but those were windstorms/snowstorms doing the work instead of me. I was very happy with the results.
Jungle of radishes:

Unfortunately everything started to move. Nothing like a landslide or such, it was erosion. As the worms and critters were digging and opening tunnels, they were loosening it. When it was dry, worm castings turned into hard soil balls and rolled down the hill side. When it was wet, worms were busy digging new tunnels, but newly formed topsoil was not able to hold against water and gravity. Pathways were covered with foot-deep soil and leaves after any major rain event. I put more leaves and many layers of branches and I was able to stop erosion from happening. Unfortunately, this solution turned into a problem. It stopped erosion, but the branch layer was 2 meters (6ft) deep. I gave up and let the invasives take over the show, wild blackberry and tree of heaven. I can’t get even get in or walk on pathways, but it stopped erosion immediately. Part of the garden turned into a safe zone for birds and other critters. Unfortunately, occasional blackberry harvest is all I can get.
Soil balls:

For my second attempt, I tried to create a table top hugel bed with a reservoir. Water is always an issue for this south facing slope. Reservoir didn’t work and table top hugel design didn’t perform as intended. I came up with solutions such as putting a drip line over hugel and now it performs quite good, but the eventual solution was complicated and also required watering. I want something simple, something straightforward that can be repeated with ease. The solution that I am seeking might not be simple for initial set up, but it should not require any major burden to get meaningful harvests.
Table top hugel:

This is my third attempt. I am terracing! This solution is very simple and straight forward. My terraces will not be as impressive as what Incas did or Filipinas, but there are no reasons for it not to work.
As always, I have limited access to most of potential resources:
Very limited budget
Limited available time – I am busy as usual
Limited external labor input – can’t effort it at the moment
Limited farm resources such as manure, straw and hay – cost prohibitive to bring in
No wood chips (nobody does that), no grass clippings (all parks are adjacent to major roads) or leaves (can’t get any more permits recently, leaves from parks are mixed with all kinds of trash)
No concrete – can’t use concrete without permit and they don’t give permits.
No excavator – can’t afford and, again, permits.
No humanure – I just don’t like it.
On the other hand, I have access to stones, rocks and a lot of clay, wastes from the garden, occasional help for labor, a lot of expired dog/cat food, coffee grounds and some kitchen scraps. I have free access to many stuffs that permies would avoid such as chemical fertilizers (funny story) and mostly avoid such as cardboards. I am going to use these terraces for food production, so chem’s or cardboards will not be used. Himalayan salt and fish scraps will be added for micronutrients and mushroom slurries will help to turn compacted clay into top soil. I have 20 bags of aged manure, which makes me feel lucky.

It is going to be a repetitive process and very likely that it will span a couple of years. I want to document and demonstrate how it begun. Nothing very impressive or jaw dropping. This is the story of how I turned a “impossible” land into a vegetable and fruit garden with a budget of roughly 8$ per square meter (1$/ft2 - 42tl/m2) for materials and a lot of exercise for labor (45 days).

It is going to be a very long, boring and mundane work. If I let my inertia free, it has a potential to burn me out. So instead of focusing on the results far in the future, I divided the project into smaller pieces. Each piece will be standalone. In other words, instead of building a 100 m long wall and then working on soil the next year, I am going to complete a 10 m section and get some produce to enjoy. If I feel like it, I will continue. As they say, start small.

There is a thin layer of topsoil that formed by my initial experimental endeavors. Eventually I will need to create top soil. The best method to turn this terrible clay and stone mixture is hugel beds and I have some experience with hugels and buried wood beds. Also, RedHawks soil treads are immensely helpful. I think buried wood beds works better than mostly or totally aboveground hugelbeds for the region I live in. They are, as hugels, are the best tools to build soil if you are into digging.

Initially I cleared the area from brambles and marked the area where I will be building the dry-stone wall. It will be no higher than 1m (3ft) and will have a minimum thickness of 50 cm (1,6 ft). Just rule of thumb.

As I started to lay down stones, I used clay from the hillside to fill the gaps between stones. I have had problems with snails and they love cool dark places between stones. I had to take down a 25 m dry sacked wall as it turned into a snail and slug factory. I am no expert on dry-stacking, but I tried to place each stone locked in place by other stones. It turned out to be steady.

After I finished my work with the wall, I leveled out the terrace area. Topsoil is reserved for future use. I need to fill some pits in the garden from previous projects, so excess subsoil was separated. The white tarp you see in the pictures are put to protect subsoil from getting rained on. Clayey soil gets very heavy and sticky when wet.

This project is not “hugel culture on contour”. I am not going to go into why I think it is a bad idea. This is a project of terracing a slope-side but instead of importing topsoil for each 60 cm deep bed, I am using permaculture techniques to create my own top soil. Moreover, I am going to divide the terrace into 4-5 m parts in the longitudinal direction. Each part will be separated with a wall of original subsoil of 50cm to 1m thickness. It won’t be visible, but it gives me opportunities to experiment. This part of the terrace has a utility line cutting through. In one part I will be digging in 30 cm deep steps. The other part will have a constant depth of 60-75 cm’s. Both will have packed earth of 40-50 cm thickness on the wall side.

Fist 30 cm deep step:

While I was digging, I came across some decomposing roots and buried pieces of wood. I found them interesting as new roots were using them as a highway through hard clay.
Through a decomposing root:

opened a bit:

Through a buried branch

This picture is to give an idea about the soil I am dealing with. Please discard the top third and bottom quarter of the picture, they don’t show the soil profile. As you can see, top 20-30 cm of soil has roots. The very top 10 cm of soil has a darker color. There are no or very few roots below 30 cm mark, since clay was impermeable. I realized that it was bone dry, even though the whole area was covered with leaves, branches and bramble for over 4 years. So, evidently rain cannot penetrate more than a foot deep.

After the digging was complete in the first part, it was time to fill it. The first to go in was invasive stuff. My first hugel beds were 80% wood and 20% soil, which turns out to be a very common mistake. Some hugelculter images in the internet can be misleading. It was very useful at promoting wildlife, but not so good for veggies. Now, I aim for 40% wood, 30-40% soil, and rest is topsoil, manure etc. I aim for 50-60% for underground wood beds and include more of greens. I add a thick layer of topsoil mix (topsoil, compost, leaves and coffee grounds) on those beds each year anyways. I put larger sized bits of wood over the “invasive layer” and gaps are filled with coffee grounds and soil. It is thoroughly watered (flooded couple of times) after it is covered with a 10 cm thick soil layer. Some can claim that flooding and adding green materials such as coffee grounds and fresh green leaves of invasive species can create an anaerobic environment, but this layer will be alive with all those earthworms and such. Wood will absorb any excess water and oxygen can travel to this depth quite easily if the soil is alive. This concludes the first layer.
Digging is complete:

Bigger sized stuff:

First layer complete:

Second layer is built in a similar fashion, but this time with smaller branches and lack of invasive plants. I was planning to add kitchen scraps from a nearby restaurant, but the deal was delayed, and I tried to compensate that by adding more coffee grounds and green waste from fall cleaning.
Green waste:

The final layer is the topsoil-mix. Topsoil that was put aside, was mixed with fall leaves, coffee grounds, manure. It has a thickness of 20-30 cm’s to compensate the soil settlement that is going to happen in the first year.

For the constant-depth buried wood bed, I wanted to test some ideas.
Constant depth bed:

I think wood of some alien species act as if bad wood while they are not so problematic in their native environment. Tree of heaven is an example for my situation. If you bury it, it is not going to rot. So, years back, I separated bad wood and made a pile for future biochar projects. Funny thing to see them getting colonized slowly by fungi. Even though I don’t know their names yet, I know which local fungi is compatible with whichever “bad wood”. I added some colonized branches for my hugel-raised beds, and they made a substantial impact. Here are the pictures of some colonized tree of heaven

and walnut (not 100% sure about this one though, can’t remember) branches:

Built a low tunnel to prevent crows from digging and future winter protection:

After all is complete, first delivery of green waste (kitchen scraps and veggies from restaurant).

Built a compost pile and the goal is to spread it before spring-summer planting.

What’s next? I am going to build various compost piles for future terraces. Hopefully some biochar will be added to terraces. I am going to flood these beds for couple of times when excess rainwater is available, so that those dry logs can absorb more. Winter is here!

Last but definitely not least. Thanks to everyone who helped this come true: all the folks here in permies for sharing their experiences and trials, learned a lot. Thanks for this forum environment and hard work :) Thanks to all that helped digging! And thanks for piles of coffee grounds, starbucks!

I like it. Very well done. I have many similar slopes that I must start working with. The few flat zone 1 & 2 spots here are already well underway. Have the same basic terraced hugelkultur plan as you showed. Thanks for sharing.

Good looking dog too!

Argue for your limitations and they are yours forever
https://permies.com/t/82998/household-encyclopedia-info

Thank you so much for this post! I also have slope and clay, although not as extreme as yours, and have been struggling with how to deal with it, as my topsoil each year runs down the yard. I built a couple low retaining walls, to try and stop, but I LOVE the idea of incorporating the hugel beds! W fortunatly have access to free loads of compost from our town, and I have been using that to level out the layers (but moving 10 pickup loads of compost with a wheelbarrow is hard work. Like you, I have found picking a small goal and feeling the accomplishment is a great way to get a big project done!

What is your gardening zone and elevation, may I ask? And, is your soil alkaline?

Fascinating project. For reference, I don' know much about hugelkulture on hillsides, other than what I just read here. I was apprehensive while reading of your first attempts to keep leaves and organic matter on that extreme slope. My apprehension I believe came from worrying that the hillside would continue to slide. Beautiful dog by the way. I liked the way over the years you addressed issues you observed during the first years, but somehow I kept coming back to the cute dog down below that mass of organic material and clay. Then I came to Tyler's link to JACK SPIRKO's discussion of combining Hughelkulture and swales. Naively I had no notion why I worried until he described what happens when the watershed above saturates the organic matter. Jack emphasizes that scale is important, but math needs to be done to determine how much water might present to the hugel bed.
Here is a link to the Youtube portion of that link

Thanks for raising concern. We are on the same page on this actually. I gave exactly the same link Tyler shared, in the 4th post (link is: bad idea):

s. ayalp wrote:This project is not “hugel culture on contour”. I am not going to go into why I think it is a bad idea.

That being said, I guess I need to clarify my situation.
Firstly; this is not a finished project. It is the very first trial run. I am planning to repeat the process changing and upgrading design based on observations. My observation for this land is that, I can put a packed earth partition behind the dry sacked wall without raising water table (my second attempt: table top hugel). Water can not pass through the bottom clay layer (reminds me rice terraces link) in the figure: layer 8 is an impermeable layer. Besides even if it does, there are cracks in the bedrock and water will drain very well. I might have added a drain pipe to drain excess water or put a layer of plastic under the bed; but I wanted to observe how it performs before opting for more complex solutions.
It is not a swale if it is only 4-5 meters long. That's the reason why I used the utility line as an opportunity to divide the underground parts.
It is hand dug. Definitely not something similar what Sepp does with excavators. Hand dug and built rice terraces are better to compare. They do hold water and some organic matter.
Finally, I did do some calculations! It meets required factor of safety values for global stability, bearing capacity and such. I had to assume many parameters though. Heavy wet logs do not differ min FoS significantly (applied as surcharge load). On the other hand, it is not possible to achieve global stability and bearing with high water table.

Sandy Smithsson wrote:Thank you so much for this post! I also have slope and clay, although not as extreme as yours, and have been struggling with how to deal with it, as my topsoil each year runs down the yard. I built a couple low retaining walls, to try and stop, but I LOVE the idea of incorporating the hugel beds! W fortunatly have access to free loads of compost from our town, and I have been using that to level out the layers (but moving 10 pickup loads of compost with a wheelbarrow is hard work. Like you, I have found picking a small goal and feeling the accomplishment is a great way to get a big project done!

What is your gardening zone and elevation, may I ask? And, is your soil alkaline?

Zone 9b, Mediterranean climate, elevation 82 to 100 meters (terrace is located at 95-96 meters I believe). The property is located in a deep valley, we have very strong micro climates. Currently these terraces do not receive sunlight more than 5 hours. It is slightly alkaline, around 7.5. Thanks!

Wow! What a beautiful job you have done with your combo! I solved a similar problem (although on a much less steep slope) by first planting alfalfa on the slope, the deep roots helped stabilize the soil while i did my digging. It has this consequence that you are pretty much stuck with the alfalfa for life after that, it self seeds in alkaline clay and survives any amount of drought and heat once rooted. Makes a great mulch if you have time to chop and drop and always a welcome addition to the compost heap, but if you cannot spare the time to keep a hand on it you will spend your days keeping it out of your lovely beds.